Container base



FIG. 1 is a bottom perspective view of a container base showing my new design;

FIG. 2 is a bottom plan view thereof; and,

FIG. 3 is a side elevation view thereof.

The broken lines shown in the drawing views are for environmental purposes only and form no part of the claimed design.

All sides not shown form no part of the claimed design. 

The ornamental design for a container base, as shown and described. 